In relation to some diseases patients must inject a medicament on a regular basis such as once weekly, once daily or even a plurality of times each day. In order to help patients overcome fear of needles, fully automatic injection devices have been developed with the aim of making the use of the injection device as simple and safe as possible. Such devices are typically designed such that a user shall position the injection device onto the injection site and activate the device. Such activation causes the device to insert a needle into the skin, eject a dose of the medicament and subsequently move the needle into a shielded position.
Prior to the actual use of the device by an end user, the needle must be assembled with the injection device. It is desired that the user does not need to handle the needle at all which requires pre-mounting of the needle with the injection device. Prior to mounting the needle on the injection device, a number of additional process steps are typically required, for example sterilization of the needle itself. It is therefore desired to provide a needle unit which is easy to handle prior to being mounted on the injection device without risking injury to people handling the needle unit and without risking damage to the needle.
In some injection devices, the needle is protected by a penetrable cover element, for example a silicone foil like cover element, which maintains a sterile barrier around the needle itself. This flexible cover element is typically not so strong and can be easily damaged. It is therefore desired to protect the flexible cover element during handling to avoid damage to the cover which could destroy the sterile barrier effect of the cover.
A needle shield is therefore often arranged to encase the needle and any cover elements which ensure the sterility of the needle. The needle shield is often assembled together with the needle to form a needle unit. During handling of the needle unit, the shield element is locked in position with respect to the needle. When the needle is to be mounted on the injection device, the shield element needs to be removed from the needle or the needle shield needs to be unlocked so that the needle shield can be displaced with respect to the needle so as to expose the needle. One example of such a prior art device is disclosed in WO 08/077706. However, this needle unit is a complex unit comprising a number of elements including a spring. The needle unit is intended for insertion into a rigid and sterile container for maintaining sterility during storing and handling. Typically such containers are sealed off by a planar seal that needs to be manually peeled off prior to mounting of the needle unit on an injection device. Such needle unit is not easily incorporated into an injection device at the time of manufacture.
Having regard to the above-identified prior art devices, it is an object of the present invention to provide a needle unit and an injection device comprising a needle unit that are improved with regards to locking of the needle shield prior to mounting of the needle unit on the injection device and unlocking the needle shield during/after mounting of the needle unit on the injection device.
Yet additional further objects of the invention are to provide measures for obtaining needle units and injection devices having a superior performance and, at the same time, enabling manufacture at a reduced cost.